Chris Mason <chris.mason@xxxxxxxxxx> writes: > On Thu, Mar 08, 2012 at 12:20:26PM -0800, Boaz Harrosh wrote: >> I think I understand this one. It's do to the sync nature introduced >> by page_waiting in mkwrite. > > Pages go from dirty to writeback for a few reasons. Background > writeout, or O_DIRECT or someone running sync > > background writeout shouldn't be queueing up so much work that > synchronous writeout has a 2 second delay. So now we're back to figuring out how to tell how long I/O will take? If writeback is issuing random access I/Os to spinning media, you can bet it might be a while. Today, you could lower nr_requests to some obscenely small number to improve worst-case latency. I thought there was some talk about improving the intelligence of writeback in this regard, but it's a tough problem, especially given that writeback isn't the only cook in the kitchen. Cheers, Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
